Simple Formula for Surge Impedance of Horizontal Grounding Conductor

Horizontal grounding conductor is often used to obtain low grounding resistance. Simulation results of voltages and currents in a circuit including a grounding system are sometimes different from measured results because the grounding resistance depends on temperature and water content. Lightning surge characteristics of a grounding conductor are important for lightning protection design. Simple formulas for the surge characteristics of the grounding conductor are useful for engineers to estimate the influence of parameters of grounding system on lightning overvoltages. This article describes measurement results of the surge characteristics of grounding conductors for various conductor lengths and terminal conditions. This article proposes simple formulas for surge impedance and propagation velocity of horizontal grounding conductor based on the measured results. A simple equivalent circuit of grounding conductor is described. The constants of the equivalent circuit are obtained using the proposed formulas. Simulation results of voltage on a grounding grid using the proposed formulas and the equivalent circuit of grounding conductor are compared with experimental results.